The enzymatic reactions involved in Ca 2 ion transport in muscle and Na ion plus K ion transport in electric organ were investigated by rapid chemical quenching and P31 nuclear magnetic resonance spectroscopy. Fast kinetic measurements of the ATPase reactions linked to Na 1 and K 1 transport have demonstrated unusual kinetic effects which suggest that the enzyme may have some "memory" of previous events. These effects have been interpreted as evidence that phosphoryl group transfer occurs at kinetically distinct but coupled catalytic sites in accord with the dimer model for transport. Comparison of phosphoprotein formation in sarcoplasmic reticulum preparations from cardiac and skeletal muscle have shown the rates to be nearly identical implying that the slower rate of relaxation in cardiac muscle arises from a lower density of transport sites rather than a reduced rate of turnover. P31 NMR studies of sarcoplasmic reticulum have confirmed the existence of covalently bound phosphorous in membranes which are transport-viable. Similarities in the resonance spectra obtained with ATP or inorganic phosphate are consistent with kinetic observations showing the transport-linked catalytic pathways to be fully reversible. BIBLIOGRAHPHC REFERENCES: Froehlich, J. P., Sullivan, J. V., and Berger, R. L.: A chemical quenching apparatus for studying rapid reactions. Anal. Biochem. 73: 331-341, 1976. Froehlich, J. P., and Taylor, E. W.: Transient state kinetic effects of calcium ion on sarcoplasmic reticulum adenosine triphosphatase. J. Biol. Chem. 251: 2307-2315, 1976.